Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $153.32   7.141%   $164.2686   $164.27   $164.25   $164.30  
  Purchase #2 $24.39   6.556%   $25.989   $25.99   $26.00   $26.00  
  Purchase #3 $64.57   7.633%   $69.4986   $69.50   $69.50   $69.50  
  Purchase #4 $213.61   4.520%   $223.2652   $223.27   $223.25   $223.30  
  Purchase #5 $65.74   12.619%   $74.0357   $74.04   $74.05   $74.00  
  Purchase #6 $55.28   11.782%   $61.7931   $61.79   $61.80   $61.80  
  Purchase #7 $228.37   13.167%   $258.4395   $258.44   $258.45   $258.40  
  7 purchase totals = $805.28       $877.2897   $877.30   $877.30   $877.30